“NASA’s Mars Exploration Program keeps bringing us closer to determining whether the Red Planet could harbor life in some form,” NASA Administrator Charles Bolden said, “and it reaffirms Mars as an important future destination for human exploration.”
The spacecraft, Mars Reconnaissance Orbiter, has been circling Mars since 2006, and during that time, Mars — which has seasons like ours — has gone around the sun three times. Each year, MRO photographed brown streaks in the Martian spring and summer. In the colder seasons, they disappeared.
According to NASA, dark, finger-like features appear and extend down some Martian slopes during late spring through summer, fade in winter, and return during the next spring. Repeated observations have tracked the seasonal changes in these recurring features on several steep slopes in the middle latitudes of Mars’ southern hemisphere.
The images show flows lengthen and darken on rocky equator-facing slopes from late spring to early fall. The seasonality, latitude distribution and brightness changes suggest a volatile material is involved, but there is no direct detection of one.
The settings are too warm for carbon-dioxide frost and, at some sites, too cold for pure water. This suggests the action of brines which have lower freezing points. Salt deposits over much of Mars indicate brines were abundant in Mars’ past. These recent observations suggest brines still may form near the surface today in limited times and places.
“The flows are not dark because of being wet,” Alfred McEwen of the University of Arizona, Tucson said. He is the principal investigator for the orbiter’s High Resolution Imaging Science Experiment (HiRISE) and lead author of a report about the recurring flows published in Thursday’s edition of the journal Science. “They are dark for some other reason.”
A flow initiated by briny water could rearrange grains or change surface roughness in a way that darkens the appearance. How the features brighten again when temperatures drop is harder to explain.
“It’s a mystery now, but I think it’s a solvable mystery with further observations and laboratory experiments,” McEwen said. “The best explanation for these observations so far is the flow of briny water,” McEwen added.
Mars, which is located at least 35 million miles farther from the sun than our planet, is far colder than Earth. But if water is thick with salt and other minerals, its freezing point would be lower than it is for clear water here.
“These dark lineations are different from other types of features on Martian slopes,” said MRO project scientist Richard Zurek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Repeated observations show they extend ever farther downhill with time during the warm season.”
Earlier NASA discoveries revealed evidence of olden shorelines and riverbanks on Mars, but further analysis of the discoveries couldn’t provide definite proof of water flows.
Back in 2006, scientist discovered significant changes in several crater gullies. They reported that water was flowing under Mars’ surface perhaps in the form of “flash floods”. But, as it was supposed to have taken place during the winter, leaving very less chance for water to be liquid, following research has cast substantial doubt on that explanation. According to the current view, it was frozen carbon dioxide that might have been flooding.
In 2008, frozen water was uncovered below the Martian surface by NASA’s Phoenix lander. McEwen and his team published their findings in Friday’s issue of the journal Science. They reported that the streaks appeared only on steep slopes. They could be hundreds of yards long, and often resembled gullies on Earth.
Other readings showed no chemical signal on the Martian surface, leading the scientists to suggest it may dry very quickly, or be just below the upper layer of Martian dust.
“We expect water on Mars to be briny, to be salty, because we know that the surface is salty from all of the past landers and rovers,” said McEwen. “Furthermore, the salt serves to depress the freezing point of the water, so in places where it’s below freezing, we see this activity, it is still plausible for that to be salty water.”
“What makes these new observations so interesting is they occur at much lower latitudes [closer to the equator], where temperatures are much warmer and where it’s actually possible for liquid water to exist,” said Arizona State University geophysicist Phil Christensen, one of the scientists who studied the images beamed back from the orbiter. [via NASA.gov, ABC News and International Business Times]